1. Field of the Invention
The present invention relates to measuring wavelength dependency of optical parameters such as the attenuation constant, the delay, the dispersion, and the like of a device under test.
2. Description of the Background Art
Conventionally, wavelength dependency of optical parameters such as the attenuation constant, the delay, the dispersion, and the like of a device under test (DUT) such as an optical fiber has been measured.
As the measuring method, methods using a Michelson interferometer and an optical network analyzer have been conventionally applied. Note that the method using the optical network analyzer is disclosed in (1) S. Ryu, Y. Horiuchi, K. Mochizuki, “Novel chromatic dispersion measurement method over continuous Gigahertz tuning range” J. Lightwave Technol., vol. 7, no. 8, pp. 1177–1180, 1989, and (2) M. Fujise, M. Kuwazuru, H. Nunokawa, and Y Iwamoto. “Chromatic dispersion measurement over a 100-km dispersion-shifted single-mode fibre by a new phase-shift technique” Electron. Lett., vol. 22, no. 11, pp. 570–572, 1986.
A constitution using the Michelson interferometer for measuring a device under test (DUT) is shown in FIG. 8. Light emitted from a light source 100 is separated into a reflected component and a transmitted component by a semi-transparent mirror 102. The reflected component transmits through a DUT 104, is reflected by a mirror 106, transmits through the DUT 104 again, and returns to the semi-transparent mirror 102. The transmitted component transmits through a variable delay line 108, is reflected by a mirror 110, transmits through the variable delay line 108 again, and returns to the semi-transparent mirror 102. The variable delay line 108 can change the optical path length of the transmitted component. The reflected component and the transmitted component having returned to the semi-transparent mirror 102 are multiplexed. At this moment, interference occurs. The light multiplexed by the semi-transparent mirror 102 is detected by a photodetector 114 through a mirror 112, and is converted into an electric signal. A processing unit 116 measures the wavelength dependency of the optical parameters of the DUT 104 based on the electric signal. Namely, the wavelength dependency of the optical parameters of the DUT 104 is measured using the interference between the light transmitting through the DUT 104, and the light transmitting through the variable delay line 108.
A constitution of a measuring system using the optical network analyzer for measuring a device under test (DUT) is shown in FIG. 9. Light emitted from a wavelength variable light source 200 is intensity-modulated by a light intensity modulator 204 based on a signal fIF of a reference high frequency signal source 202, and enters into a device under test 206. The light entered into the device under test 206 transmits through the device under test 206, is detected by a photodetector 208, and is converted into an electric signal. The electric signal is amplified by an amplifier 210, and the phase and the amplitude is compared with the signal fIF by a phase/amplitude comparator 222. As a result of the comparison, the phase and the amplitude are obtained, are converted into digital signals by an A/D converter 224, and are processed by a data processing block 226, and the wavelength dependency of the optical parameters of the device under test 206 is measured. Note that the phase/amplitude comparator 222, the A/D converter 224, and the data processing block 226 are parts of an network analyzer 220.